Organic optoelectronic components such as, for example, organic light emitting diodes (OLEDs), OLED displays or organic solar cells or photovoltaic cells (organic photovoltaic (OPV) cells) can be protected both against ingress of water and oxygen (encapsulation) and against mechanical contact and damage by the application of protective layers and packaging.
There are various methods for the encapsulation and mechanical packaging of organic optoelectronic components (e.g. OLEDs) on glass substrates.
One method is based on encapsulation with the aid of glass cavities. In this technique, a glass cover is adhesively bonded onto the component (device) with a specific adhesive. This technique can largely prevent the ingress of harmful influences. However, in the region of the adhesive bond, water and oxygen can still diffuse into the component. As a countermeasure in this respect, water- and oxygen-binding materials (so-called getters) can be introduced into the cavity. These can absorb the water and oxygen before the organic materials are damaged. The glass cover simultaneously affords sufficient mechanical protection. However, the method of cavity encapsulation overall is very cost-intensive. Moreover, the use of (rigid) glass covers or glass cavities is not suitable for the manufacture of flexible (i.e. pliable) components (e.g. flexible OLEDs).
In accordance with another method, provision is made for sealing organic components (e.g. OLEDs) exclusively by applying thin films (thin layers or thin-film layers) against water and oxygen (so-called thin-film encapsulation). However, said thin-film layers are generally mechanically very sensitive and should (just like the components itself) be protected against contact or scratching. This can be realized for example by areal lamination of a flat cover glass. Sufficient mechanical protection of the component and the encapsulation can be achieved by the glass. In this case, however, defects still occur relatively frequently, said defects being attributable to particles on the topmost layer of the thin-film encapsulation or on or in the lamination adhesive layer.
The encapsulation by means of thin-film methods is also suitable for flexible components (e.g. flexible OLEDs) on foil substrates (e.g. steel foil or polymer foil substrates). For protection against contact and damage, here for example foils can be laminated onto the substrate foil or the substrate foil can be laminated between two packaging foils. In this case as well, however, damage to the barrier thin-film layer can occur as a result of particle loading at the interface between thin-film layer/adhesive surface.
The patent application DE 10 2008 019 900 A1 presents materials and embodiments for a mechanical protective layer on the barrier layers. Said application for example also describes a lacquer spraying method as a suitable method. In that case, however, only a single-stage process without intermediate layers is described, which does not take account of the problem of particle influence on the encapsulation quality.
FIG. 1A and FIG. 1B schematically illustrate the occurrence of failures as a result of possible particle loading during the lamination and adhesive bonding of protective glasses or foils onto an organic light emitting diode (OLED) in accordance with one conventional method.
FIG. 1A shows in a first view 120 the schematic construction of an organic light emitting diode (OLED) 100 including a substrate 101, a first substrate-side electrode 102 (first electrical contact or bottom contact), organic functional layers 103 and a second top-side electrode 104 (second electrical contact or top contact). For encapsulation against the ingress of water and oxygen, a barrier thin film 105 is applied on the second electrode 104. As mechanical protection, a cover plate 107 (scratch protection film) is applied at the top side and adhesively bonded to the OLED 100 (or the barrier thin film 105) by means of an adhesive layer 106 (adhesive). The adhesive-bonding process or lamination process is symbolized by the arrows 108 in FIG. 1A.
“A” to “D” in FIG. 1A denote typical classes of particle impurity (particle contamination) which can lead to damage to the OLED 100 or the barrier thin film 105: particles can lie on the barrier thin film 105 (particle “A”) or on the adhesive layer 106 (particle “B”), or they can be embedded in and below the barrier thin film 105 (particle “C”) or the adhesive layer 106 (particle “D”).
FIG. 1B shows in a second view 140 the OLED 100 after the cover plate 107 has been applied and adhesively bonded. The adhesive-bonding process or lamination process 108 for applying and adhesively bonding the cover plate 107 on the optoelectronic component 100 is usually effected by exerting mechanical force or pressure on the components to be connected. FIG. 1B shows that the particles (particles “A”) situated on the barrier thin film 105 and the particles (particles “B” in FIG. 1B) situated on the adhesive layer 106 are pressed into the barrier thin film 105 by the adhesive-bonding process or lamination process 108. It is furthermore shown that particles (particles “D”) embedded in the adhesive layer 106 can also be at least partly pressed into the barrier thin film 105 during the adhesive-bonding process 108. Furthermore, particles (particles “C”) embedded in the barrier thin film 105 may also be pressed, by the pressure which is exerted during the adhesive-bonding process 108 and which may be transmitted via the barrier thin film 105 to the particles (particles “C”) embedded therein, further into the barrier thin film 105 and possibly as far as the underlying layer (i.e. the second electrode 104 in the embodiment shown), or can even be pressed into the latter, which is shown in FIG. 1B.
Illustratively, during the lamination of the cover layer 107, on account of the small size and thus small bearing area of the deposited or embedded particles, greatly localized peaks of the pressure distribution may occur at the particles (in particular at the underside of the particles) since the pressure is inversely proportional to the bearing area. These local pressure peaks may in turn lead to a greatly localized mechanical loading on the layers adjoining the particles (in particular the underlying layers). Consequently, the particles may damage the barrier thin film 105 and possibly also one or more of the underlying layers (e.g. the second electrode 104, the functional layers 103 and possibly even deeper layers) as a result of the greatly localized mechanical loading.
In particular as a result of the mechanical damage to the barrier thin film 105, further damage to the OLED 100 (in particular the organic functional layers 103) may occur as a result of ingress of harmful chemical constituents such as e.g. water or oxygen into the OLED 100. This may lead to impairment of the function or even to the total failure of the OLED 100.
The effects during encapsulation and packaging as described above with reference to FIG. 1A and FIG. 1B using the example of an organic light emitting diode (OLED) can also occur in the case of other optoelectronic components, in particular other organic optoelectronic components, which are encapsulated and packaged in the same or a similar manner.